Progesterone is strictly a growth-promoter for mammary epithelium. It is not required for its differentiation. Modified insulin derived from insulin-Sepharose can stimulate ornithine decarboxylase activity in liver of insulin-resistant mice in vivo. BIBLIOGRAPHIC REFERENCE: Topper, Y.J., Oka, T., Vonderhaar, B.K. and Wilchek, M.: An insulin-derivative with biological activity greater than that of native insulin. J. Cellular Physiology 89: 647-649, 1976.